Graduate Thesis Or Dissertation
 

Net production, movement, and food of cutthroat trout (Salmo clarki clarki Richardson) in three Oregon coastal streams

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  • Unfished populations of cutthroat trout in three small coastal streams in Oregon were studied from April of 1962 until November of 1963. Population size, growth rate, and net production were estimated for study areas in each stream. The nature of seasonal movement patterns within the study areas and at fish traps was examined. Food habits of trout during the time of emergence and early growth of coho fry were studied. The mean annual biomass of cutthroat trout for all streams was 4.2 grams per square meter. Growth in length was greatest in April and May and least in October and November. Net production averaged 4.1 grams per square meter for the three streams. Growth rates were about equal in the three streams, but production levels were about 20 percent higher in one stream. Upstream migrations of trout occurred from late October until March, with a maximum in December. Kelts returned downstream from December to April with the greatest numbers in January and February. More than 90 percent of the downstream movement of smolts occurred in February, March, April and May, with numbers being consistently greatest in April. Two-year-old smolts dominated the run in the two larger streams, while one-year-old smolts did so in the smallest stream. Small tributaries of the study areas were found to be very important to cutthroat trout reproduction. Young trout were noted to leave the tributaries at about one year of age. Trout 150 mm in length that had never left the study streams were found in a gravid condition near redd sites. Food samples taken during the period of coho fry emergence and early growth failed to show that cutthroat trout were important consumers of young coho. Aquatic arthropods were consistently an important part of the diet; earthworms decreased in importance; and terrestrial arthropods increased in importance during the period from February to June.
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